The present invention relates to a flow control system to be used with a surgical handpiece, which is primarily utilized for the removal of organic tissue from an enclosed or semi-enclosed operative site. The flow system is particularly adapted for use in the removal of a cataract lens in the human eye, and thus, by way of illustration, will be described in that context.
Early techniques for cataract surgery involved intracapsular extraction, in which the lens, enclosed in its complete capsule, is entirely removed by making a 180.degree. incision in the eye so that the cornea could be lifted and the lens removed as a whol. Current techniques involve extracapsular extraction in which the only lens contents and a portion of the lens capsule is removed. Typically the posterior capsule is left intact with the anterior capsule being partially or totally removed. Extracapsular cataract extraction is achieved by making a small incision in the eye so that the tip of a surgical handpiece can be inserted into the anterior chamber of the eye to access to the diseased lens.
Several types of handpieces currently are used in the extracapsular cataract extraction. Some handpieces use rotating or oscillating cutting devices to chop the diseased lens into small pieces while, other handpieces use phacoemulsification techniques wherein an ultrasonic needle is inserted into the lens so ultrasonic energy can affect the disintegration or emulsification of the lens. During or after disintegration of the lens, the fragments are removed from the eye.
Regardless of the technique used for fracturing and removing the lens, a cortex layer on the inner wall of the lens capsule must be removed from the operative site. This removal is typically accomplished using a handpiece which includes a tip formed as an elongate, rigid tube surrounded by a sleeve spaced from the tube, thus providing two separate flow channels. Washing fluid is introduced through the hollow sleeve at a constant pressure. This introduction of fluid, which is called "irrigation," provides a replacement for fluid and material withdrawn or lost from the eye chamber. Fluid and suspended cortex material is withdrawn from the anterior chamber through the rigid tube. This withdrawal is called "aspiration". A handpiece simultaneously irrigating and aspirating the eye is called an "IA handpiece." In practice, the tip of the IA handpiece is used to rub or abrade away the cortex layer. In some instances the irrigation and aspiration can be used to aid the cortex removal.
It is of particular importance that, during the operation, the pressure of the anterior chamber be maintained within a certain range of values, since otherwise various portions of the eye could be damaged. For example, a collapse of the anterior chamber could result in either the iris, the endothelium layer of the cornea, or the posterior capsule being damaged.
In order to insure against the collapse of the anterior chamber, complex flow control systems have been developed for supplying fluid to, and removing fluid and residue from, the handpiece flow channels. Many utilize flow transducers, a series of valves, electronic flow control devices, constant volume pumps and, of course, an electric power source for the system. These systems are quite complex and expensive. Furthermore, the complexity of these systems requires that support personnel obtain extensive training to adequately assist the doctors during eye surgery.
Other flow control systems are substantially simpler and more easily regulated by operating room personnel. They regulate the fluid flow pressure principally by adjusting the height at which an irrigation fluid source is supported above the eye. Most importantly, however, these systems use constant displacement pumps (often peristaltic pumps) to provide the suction for aspiration of the system. Periodically during the operation, the opening in the tip of the handpiece, through which the aspiration proceeds, may be occluded by large fragments of lens material or the capsule wall itself. During such occlusion, fluid is prevented from entering the aspiration channel. However, the system's constant displacement pump continues to operate, gradually constricting the resilient tubing utilized by the system until the vacuum reaches dangerous proportions. This problem is particularly acute because the total volume in the anterior chamber of the eye is very small in relation to the overall volumetric constriction of the tubing. If the resulting vacuum is now somehow released before the occlusion is dislodged from the aspiration channel, the tubing may suddenly spring back to its normal diameter, rapidly withdrawing fluid from the anterior chamber and drawing the enclosing tissues toward the handpiece tip. Either tissue contact with the aspirating channel of the handpiece, or the rapid deformation of the anterior chamber could cause irreversible injury to the patient' s eye.
The flow control system for which the present pinch valve is primarily designed uses a low-cost, disposable, constant pressure vacuum source. Furthermore, the vacuum source is mechanically operated, and therefore not dependent upon an outside electrical power source; thus adding to the system's reliability.
In the event that the aspiration channel of this system is occluded, the vacuum source continues to supply only that amount of negative pressure previously supplied to the system, thus obviating the need for the vacuum release devices utilized by other irrigation/aspiration systems. However, if a greater vacuum is needed in order to clear the occlusion from the aspiration channel, this system contains a separate, low-cost, high-vacuum source which can be adjusted to provide only that vacuum necessary to dislodge the occluding matter. Although this vacuum is sufficient to clear the aspiration channel, it is not so great as to pose the danger of rapidly decompressing the anterior chamber. In the event that a safe level of vacuum is not sufficient to clear the aspiration channel, the system provides a means for the momentary reversal of the flow in the aspiration channel in order to dislodge the occlusion.
In contrast to the more complex and expensive irrigation/aspiration systems described above, a simpler irrigation/aspiration system has heretofore used a finger pinch valve to control the aspiration of the system and a separate clamp to control the irrigation of the system. This manual operation has required the surgeon to use one hand to control or adjust the system. This restriction on the use of one of the surgeons hands has limited the commercial viability of this simpler, less expensive system.